This invention relates generally to the packaging of articles such as cans, bottles and the like to make multi-unit packages and more particularly to the packaging of these articles by applying a sheet of film over a group of the articles in a paperboard tray, causing the film to bond to the tray by heating the film, or subsequently heat-shrinking the film to tightly hold the articles in the tray and make a unitary package.
Machines which package articles in paperboard trays by applying a sheet of film over the articles and bonding the film to the tray are known in the prior art. Such machines have been produced by Huntingdon Industries of Bethayres, Pennsylvania, under the trade names "WrapCap" and "PacCap" in accordance with the disclosure in my prior U.S. Pat. No. 3,890,763, issued June 24, 1975 and my copending U.S. patent application Ser. No. 683,611. In these machines, open top paperboard trays are loaded with the articles to be packaged and moved along a prescribed path. As the trays are conveyed along the path, a sheet of heat shrinkable film is dispensed over the articles in the tray and wrapped tautly down over the articles into juxtaposition with opposite sides of the tray by a plurality of flight bars moving along an endless path.
In one version of such machine, an appropriate adhesive such as a hot melt glue is applied to the side walls of the tray prior to the placement of the film thereover. The flight bars in the glue version press the film against the opposite sides of the tray to which the adhesive has been applied with sufficient pressure to cause the adhesive to bond the film to the tray.
In another version of the machine, the material of the film itself, rather than a separate adhesive, is used to bond the film to the tray. To do this, the film must be able to form a fiber tearing bond with a cellulosic tray under sufficient heat, time and pressure. The flight bars in the heat weld version press the film against the opposite sides of the tray while heating the film. The film is thusly held for a sufficient length of time for the film to weld itself to the tray side walls with the fiber tearing weld.
In both versions of the machine, the film is severed between trays to separate the film covered trays from each other. The resulting film sheet covering the articles and bonded to opposite side walls of the tray keeps the articles in the tray. Typically, the film used is heat shrinkable. This allows the thusly formed package to be passed through a heat tunnel so as to shrink the film and tightly lock the articles in the tray.
While both versions of the machine produce a package which has certain advantages, such as the film not being on the bottom of the trays, the resulting package has some drawbacks in that it is necessary to leave an unattached portion of the film below the point where the film is bonded to the side walls of the tray. This portion of the film, typically called the skirt, is loose so that it can become entangled in handling equipment in subsequent package handling operations. Further, the skirt also tends to become wrinkled during the heat shrinking operation and obscure any printing on the sidewalls of the tray.